Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $246.68   9.579%   $270.3095   $270.31   $270.30   $270.30  
  Purchase #2 $176.81   12.461%   $198.8423   $198.84   $198.85   $198.80  
  Purchase #3 $225.68   5.146%   $237.2935   $237.29   $237.30   $237.30  
  Purchase #4 $202.98   5.469%   $214.081   $214.08   $214.10   $214.10  
  Purchase #5 $116.75   12.539%   $131.3893   $131.39   $131.40   $131.40  
  Purchase #6 $95.81   7.155%   $102.6652   $102.67   $102.65   $102.70  
  Purchase #7 $244.40   4.377%   $255.0974   $255.10   $255.10   $255.10  
  7 purchase totals = $1,309.11       $1,409.6782   $1,409.68   $1,409.70   $1,409.70